In the field of simplified test kits based upon immunoassays, for example, pregnancy tests and tests for infectious diseases, it is conventional to run a positive control and a negative control as well as the patient sample.
The point of the positive control is to produce a detectable indication, for example a color change, that will always occur if the reagents are functioning properly. That is, the positive control indicates the device is functioning in a way such that, if the test antigen were present in the patient sample, there would also be a similar detectable indication produced. On the other hand, the point of the negative control is that occasionally, some error or interferent will be introduced such that, even in the presence of the target antigen, the test is defective even though the positive control may produce a visual indication suggesting (erroneously) that all is well.
In the early stages of development of these devices, the positive and negative controls were simple color changes over a target area. A problem with such devices is that a simple color change can be confusing--does the change in color of a particular dot mean the test is OK, or does it mean it is not OK? Partially in response to this need, the test devices have become more sophisticated. One type, for example those described in EPA Publication Nos. 217,403; 264,036; 249,418 and 335,244, causes the positive control area to produce a color change in conjunction with the patient sample area to give a combined symbol that represents either a "negative" condition or a "positive" condition. Not surprisingly, the symbols produced are "-" and "+", respectively. This achieved by having the positive control always form the horizontal cross-bar, which without an antigen in the patient sample, produces a "minus" sign. However, any targeted patient antigen present causes the vertical bar to also develop color, converting the "-" into a "+".
Such a "+" and "-" system may be satisfactory when testing for a single antigen, but it is not particularly useful in combination tests, such as periodontal assays, that test for more than 1 antigen at once. Such a combination of tests needs a positive control for each antigen being tested, and a corresponding symbol representation for that separate positive control. Furthermore, the conventional "+" and "-" system requires the negative control, which it not used with the "+" or "-", to form some unrelated symbol somewhere else, if the test fails, for example, because the antibodies have denatured. aforesaid EPA 217,403 and its U.S. counterpart U.S. Pat. No. 4,916,056 do not even produce a representational symbol, for an invalid test. Instead, if the test is invalid, NO specific, predetermined and connected signal is produced whatsoever (as shown in FIGS. 3A, 4A, 6A and 7A in the '056 patent.) This is unsatisfactory, as such a result leaves a question in the user's mind as to what actually happened.
Therefore, there has been a need prior to this invention for an immunoassay test device that causes positive controls for multiple antigens to combine together to form a meaningful symbolic indication whether the test is performing satisfactorily or not, for all the antigens. There has been a further need to combine the negative and positive controls into one general location to produce a symbolic representation that covers all aspects of the device's satisfactory performance, and not just the positive control's satisfactory performance.